در مورد مدیریت بهینه طبقه ای از سیستم های زیست محیطی و اقتصادی آبزیان

This paper studies aquatic ecological–economic systems such as the Chesapeake Bay. The stability of such ecological–economic systems depends on the successful functioning of a small number of generalist species in a wide range of ecological and economic conditions. We first characterize the persistence of such systems. We then analyze the dynamic and the stochastic aspects of the resource allocation problem faced by the manager of an aquatic ecological–economic system. This manager wishes to allocate his scarce financial resources optimally among economic activities and the maintenance of the generalists species of the aquatic ecological–economic system.

Economists and ecologists now agree that the problems associated with desertification, habitat loss, and species extinction, are global in scope. As well, researchers also concur that the solutions to these problems that have been proposed by scholars working within the confines of economics and ecology are not working because these solutions are, inter alia, narrow in scope. This recognition has led to a considerable amount of interdisciplinary research between economists and ecologists. 1 This body of research has emphasized the fact that ecological and economic systems are jointly determined. The clear implication of this is that if we are to truly comprehend the many interdependencies between such systems, then we must study these systems jointly. Despite the significance of this implication, a number of issues relating to the functioning of jointly determined ecological–economic systems remain poorly understood. Consequently, the objective of this paper is to study aspects of the stability and the optimal management of a class of aquatic ecological–economic systems; examples include coastal and estuarine ecological–economic systems such as the Chesapeake Bay in USA. As Costanza et al. (1995) have noted, the distinguishing feature of these ecological–economic systems is that their stability depends on the successful functioning of a small number of generalist species in a wide range of ecological and economic conditions. In the Chesapeake Bay, for instance, the various species of submerged aquatic vegetation2 make up an important part of this set of generalist species. There are many ways in which one can think of the stability of an ecological–economic system. Indeed, as Stuart Pimm (1991, pp. 13–14) has noted, ecologists have used the word stability to refer to a number of different concepts. These concepts include the notions of persistence, resistance, and variability. Because of the many meanings of stability, the question as to which specific meaning one should use in a given situation depends greatly on the context that the researcher is interested in studying. In this paper, we are interested in studying the optimal management of aquatic, i.e., coastal and estuarine ecological–economic systems like the Chesapeake Bay. For these ecological–economic systems, it is essential that management focus on how long the composition of the small number of generalist species (in the Chesapeake Bay the various species of submerged aquatic vegetation), that collectively determine the stability of the ecological–economic system, lasts. Now, persistence refers to “how long a variable lasts before it is changed to another value” (Pimm, 1991, p. 21). 3 This tells us that the stability concept that we should be concentrating on is persistence. This is the reason for focusing on persistence in this paper. Although, ecologists and economists have been interested in the management of ecological–economic systems, they have gone about the task of managing such systems in their separate ways, each behaving as if the other did not exist. For instance, O'Neill and Kahn (2000) point out that the current paradigm in ecology views humans as an external disturbance on the natural ecosystem and that the current paradigm in economics sees ecosystems as external to human societies. This way of viewing the world has led economists to think of “the environmental resource-base as an indefinitely large and adaptable capital stock” (Dasgupta, 1996, p. 390, emphasis in original). Similarly, this isolationist attitude to the management of ecological–economic systems has led ecologists to view “the human presence as an inessential component of the ecological landscape. This has enabled them to ignore the character of human decisions and, so, of economics” (Dasgupta, 1996, p. 390).4 Fortunately, this unhappy state of affairs has begun to change. In particular, recent research in ecological economics has led to a number of new insights into the management of ecological–economic systems.5 However, this research and the attendant insights into management that this research has yielded, have both been very recent. Consequently, there are a number of outstanding research questions about the optimal management of jointly determined ecological–economic systems. In this paper, we shall study the following hitherto unanswered question: How should the manager of an ecological–economic system allocate his scarce financial resources so as to optimally manage coastal and estuarine ecological–economic systems whose persistence is determined by the successful functioning of a small number of generalist species in a wide range of ecological and economic conditions? The rest of this paper is organized as follows. Section 2 provides a mathematical characterization of persistence for coastal and estuarine ecological–economic systems such as the Chesapeake Bay. Section 3 analyzes the above described resource allocation problem faced by the manager of an aquatic ecological–economic system. Finally, Section 4 concludes and offers suggestions for future research.

In this paper, we studied the optimal management of jointly determined CEEs. The distinguishing feature of these ecological–economic systems is the fact that their stability (persistence) depends on the successful functioning of a small number of generalist species in a wide range of ecological and economic conditions. We first provided a mathematical characterization of the persistence of CEEs. To the best of our knowledge, this task has not been undertaken previously in the literature. We then studied the dynamic and the stochastic aspects of the resource allocation problem faced by a manager who is interested in the ecological and the economic aspects of the management problem. Our analysis leads to three salient policy conclusions. First, when considering the management of CEEs, it is important to take those steps which ensure that the composition of the small number of generalist species is maintained. In the context of a CEE such as the Chesapeake Bay, this means that it is salient to ensure the well-being of the various species of submerged aquatic vegetation. This is because the communities comprising the submerged aquatic vegetation are essential feeding and refuge areas for a number of species. Moreover, these communities “have been shown to play a significant role in modulating nutrient and sediment cycling in littoral regions of the Bay” (Costanza et al., 1995, p. 107). Second, in determining the optimal division of the exogenously given budget between the generalist species of the CEE, the manager should not consider the magnitude of the available budget. In other words, the decision rule for allocating this budget between the generalist species of the CEE is invariant to fluctuations in the actual level of the budget. Finally, the manager of a CEE should permit economic activities to continue up to a point and no further. At this point, the cost of economic activities equals the right-hand side of Eq. (12). To see the merits of this kind of an approach to the management of CEEs, consider the effects of mismanagement in a particular CEE, namely, the Chesapeake Bay. The economic importance of this Bay stems primarily from the presence of species such as the American oyster, the striped bass, the American shad, and the blue crab (Cumberland, 1990). In recent times, the numbers of these species have declined dramatically. As noted by Costanza et al. (1995, pp. 118–119), this is because of “a combination of overfishing and mismanagement of … submerged aquatic vegetation …” The analysis of this paper can be extended in a number of directions. In what follows, we suggest three possible extensions. First, this paper analyzed the case of uncertainty associated with the effects of managerial actions for a single species only. A more general approach would involve working with two stochastic differential equations, corresponding to the two sources of uncertainty in the management problem. Although, it is unlikely that this more general formulation will lead to closed-form solutions, a numerical analysis of this more general model is likely to yield useful policy insights into the optimal management of jointly determined CEEs. Second, it might be useful to analyze a version of the CEE management problem in which the total number of members in each of the two-generalist species, i.e., n1 and n2, vary over time. Finally, the analysis of this paper can be made richer by studying the effects of specific price and quantity control instruments on the well-being of an ecological–economic system as measured by persistence or, depending on the context, an alternate stability concept such as resistance or variability. Analyses of these aspects of the problem will provide additional insights into the optimal management of jointly determined ecological–economic systems.